Understanding the properties of gravity at the quantum level has been the subject of intensive research for almost a century.
Some progress has been gained in the infra-red (IR) domain, where one considers quantum gravity (QG)
on the same footing as the other fundamental interactions, with gravity being mediated by
a massless spin-2 quantum field, the graviton [1]}, [2]}, [3]}, [4]}. This understanding
of weakly-coupled gravity was obtained using standard QFT methods developed during the 60's and early 70's, such as quantization, renormalization, and regularization of Yang-Mills theories [5]}. It was learned then that pure QG is finite at one-loop,
but divergences start appearing at two-loop level in pure gravity, while the inclusion of matter interacting with gravity presents divergences
already at one-loop, leading to the conclusion that QG is non-renormalizable [6]}.
On the other hand, the progress made on effective field theories, which brought a deeper understanding of its philosophy and
calculation machinery, allowed to perform loop-calculations even for non-renormalizable theories, such as chiral
perturbation theory [7]}. This in turn paved the way to perform reliable calculations for perturbative quantum gravity (pQG) at the loop-level [8]}, [9]}, [10]}, [11]}.
